CML and ECL gates typically comprise a first pair of differentially coupled transistors having collectors connected to a first supply voltage, bases coupled to receive an input signal and an inverted input signal, respectively, and emitters coupled to a second supply voltage by a current source. These first differentially coupled transistors provide high impedance inputs at their bases, voltage gain within the gate, insignificant power supply noise generation due to the elimination of current spikes, and nearly constant power supply current drain Some ECL gates may include an enable-disable circuit comprising a second differentially coupled transistor pair, having one collector-emitter path coupled between the emitters of the first differentially coupled transistor pair and the current source and the other collector-emitter path coupled between the collector of one of the first differentially coupled transistors and the current source. The bases of the second differentially coupled transistor pair are coupled to receive enable and inverse enable signals, respective.
For the ECL gate, first and second emitter follower transistors have their collectors connected to the first supply voltage, their bases connected to one of the collectors of the first differentially coupled transistor pair, respectively, and an emitter coupled to the second supply voltage by a resistor The emitter follower transistors restore the logic level and provide low output impedance for good line driving and high fanout capability.
However, for gates having series gating such as the enable-disable circuit described above the magnitude of the output signal skew in response to the digital input signal caused by the capacitance of the circuit on the collector of one of the first pair of differentially coupled transistors may cause problems in the circuits to which the output signal is provided.
Thus, what is needed is an ECL gate having substantially reduced output skews in response to input signals applied to a series gated circuit.